The chlorides of aluminum and tin produce nearly continuous white light when used in high intensity discharge lamps. However, chlorine is highly reactive with tungsten resulting in the destruction of the lamp electrode. It is possible to protect the electrodes by adding iodide to the lamp but this results in loss of efficacy.
Electrodeless lamps using solenoidal electric fields to support high intensity discharges provide an opportunity to use lamp ingredients which would otherwise cause destruction of the lamp electrodes. An electrodeless high intensity discharge solenoidal electric field (HID-SEF) lamp is essentially a transformer which couples radio-frequency energy to a plasma, the plasma acting as a single-turn secondary. A magnetic field, changing with time, creates an electric field within the lamp which closes completely upon itself and which excites the plasma to create a high intensity discharge. HID-SEF lamp structures are the subject matter of U.S. Pat. No. 4,017,764 and U.S. Pat. No. 4,180,763, both issued to J. M. Anderson and assigned to the assignee of the present invention, both patents being incorporated herein by reference.
Fills for HID-SEF lamps previously used include (1) inert gases, (2) rare earth compounds, (3) mercury, (4) metallic halides and (5) mercury halide combined with nitrogen and iodine.